The present invention relates generally to integrated circuits (ICs) and more specifically to the regulating of a power supply of an IC.
Integrated circuits (ICs) typically include many switching elements, such as transistors. These switching elements are configured to perform a variety of circuit functions.
The operation of a transistor is typically affected by its process, voltage, and temperature (“PVT”). The “process” component of PVT refers to the process of manufacturing a transistor. The process is often classified as “fast”, “slow”, “nominal”, or anywhere in between. A transistor manufactured using a fast process will transmit signals at a faster rate as compared to a transistor manufactured using a slower process. Likewise, a transistor manufactured using a slow process will transmit signals at a slower rate as compared to a transistor manufactured using a faster process. Once a transistor is manufactured using a particular process, the effect of the process is fixed. Thus, the “process” component of PVT cannot be adjusted to change the operating characteristics of a manufactured transistor.
The “temperature” component of PVT is the temperature at which the transistor operates. Similar to the process used to manufacture a transistor, the temperature at which a transistor operates affects how a transistor operates. In particular, the rate at which a transistor transmits a signal is affected by the temperature at which the transistor operates. For example, a transistor operating at a reference temperature requires a first voltage to transmit signals at a first rate. If the temperature of the transistor decreases, less voltage is needed to transmit signals at the first rate. Similarly, if the temperature of the transistor increases, more voltage is needed to transmit signals through the transistor at the first rate. The “temperature” component of PVT varies during operation of the transistor. While there is some control over the temperature of an IC, such temperature cannot be sufficiently adjusted to result in a change in its operating characteristics.
The only component of PVT that can be varied effectively during operation to adjust a transistor's characteristics is its voltage. The optimum supply voltage of a transistor varies depending on the transistor's process (e.g., fast or slow) and the transistor's operating temperature. A conventional solution to the variation in the optimum supply voltage is to set the supply voltage to a worst-case value. In transistors manufactured with a fast process or operating at a low temperature, this conventional solution often results in too much power being supplied to the transistor, with the excess power being dissipated (i.e., wasted).
As an example, if a circuit designer determines (e.g., via simulation of an IC having many transistors) that a transistor manufactured with a slow process needs 3.2 V as a supply voltage, the circuit designer may provide a supply voltage of 3.2 V to each transistor on the IC. If another transistor on the IC was manufactured with a fast process, however, that transistor might only need a supply voltage of 3.0 V. When 3.2 V is supplied, excess power is dissipated on the transistor that only needs 3.0 V as a supply voltage. As the number of transistors on the IC that were manufactured with a fast process (or are operating at a low temperature) increases, the amount of dissipated power increases.
Increased power dissipation on an IC often corresponds to an increase in IC component cost because increased packaging requirements have to be satisfied. This additional packaging results in increased cost for the IC. Also, increased power dissipation often decreases reliability of the IC.
FIG. 1 depicts a conventional method for setting the output voltage of a voltage regulator 112 in a power supply circuit 110 to provide a particular voltage Vdd 132 to an IC 130 in a system 100. A resistive voltage divider formed by resistors R1 and R2 provides a voltage-control signal V2 (or feedback signal) to the voltage regulator. Voltage regulator 112 is conventionally designed such that its output voltage VOUT is a function of the output-voltage control signal V2. Resistors R1 and R2 are located externally to IC 130 and may even be located internally to voltage regulator 112. In such a system, the manufacturer of the IC generally has no control over the specific values of resistors R1 and R2, which values ultimately determine the output voltage of the power supply circuit. As a result, the manufacturer of the IC must rely on the designers of system 100 to select appropriate values of resistors R1 and R2 to set the output voltage VOUT of the power supply circuit 110.
Therefore, there remains a need to adjust, via internal components of an IC, the voltage applied to the IC by a power supply.